Solid-state imaging device, driving method, and electronic device

ABSTRACT

Provided is a solid-state imaging device including: a pixel section configured to include a plurality of pixels arranged in a matrix form, the plurality of pixels performing photoelectric conversion; column signal lines configured to transmit pixel signals output from the pixels in units of columns; an AD converting section configured to include a comparator that compares a reference signal serving as a ramp wave with the pixel signals transmitted via the column signal line and convert a reference level and a signal level of the pixel signals into digital signals independently based on a comparison result of the comparator; a switch configured to be connected with the column signal lines; and a control section configured to turn on the switch only during a certain period of time in a period of time in which the comparator is reset and cause the column signal lines to be short-circuited.

TECHNICAL FIELD

The present technology relates to a solid-state imaging device, adriving method, and an electronic device, and more particularly to, asolid-state imaging device, a driving method, and an electronic device,which are capable of suppressing deterioration of linearity in ADconversion and quantization vertical streak caused by a quantizationerror with a high degree of accuracy.

BACKGROUND ART

A complementary metal oxide semiconductor (CMOS) image sensor can bemanufactured using the same manufacturing process as a CMOS integratedcircuit (IC), driven by a single power source, and mounted within thesame chip together with an analog circuit or a logic circuit using aCMOS process. Thus, it has several advantages in that the number ofperipheral ICs can be reduced.

For this reason, in recent years, instead of a charge coupled device(CCD) image sensor, a CMOS image sensor has attracted attention as animage sensor.

In a CMOS image sensor, in order to read a pixel signal out to theoutside, address control is performed on a pixel array section in whicha plurality of unit pixels are arranged, and a pixel signal from eachunit pixel is arbitrarily selected.

Further, in a CMOS image sensor, a column analog to digital (AD)converting circuit in which a slope type AD converting circuit isarranged in a column can be used as a circuit for performing ADconversion from an analog pixel signal read from a pixel array sectioninto a digital signal.

In this type of column AD converting circuit, when a processing speed ora frame rate is increased by increasing the number of pixels arranged inthe pixel array section, an inclination of a slope of a reference signalRAMP used as a reference voltage (a ramp-like voltage) for AD conversionbecomes steeper. Due to this influence, particularly in low-gain orlow-gradation (low-bit) reading, an AD conversion point of each columnis concentrated on a point of a slope, and thus deterioration oflinearity occurs due to the influence of power fluctuation or a verticalstreak caused by a quantization error due to low gradation.

As a technique of preventing this phenomenon, the applicant of thisapplication already proposed a technique in Patent Literature 1.

Patent Literature 1 discloses a technique of embedding a noise byincreasing a pulse width of a reset pulse of a pixel or adjusting apulse width of a reset pulse of a comparator at the time of resetreading of a vertical signal line and performing signal sampling in themiddle of a setting period of time to input capacitance of a comparatorthat compares an analog pixel signal with a reference signal RAMP.

Since it is possible to spread a reset level distribution by drivingusing this technique, it is possible to prevent concentration of energyand suppress a quantization vertical streak caused by a quantizationerror by varying an operation period of time of a column AD convertingcircuit.

CITATION LIST Patent Literature

Patent Literature 1: JP 2009-38834A

SUMMARY OF INVENTION Technical Problem

Meanwhile, in the driving using the technique disclosed in PatentLiterature 1, since signal sampling is performed in the middle of thereset settling period of time, a phenomenon that an average value of areset level is shifted at the same time when the reset leveldistribution is spread is occurs.

In a current state in which the slope of the reference signal RAMP istoo steep, in order to spread the reset level through this technique,the reset pulse of the comparator has to be released at the same time asthe reset pulse of the pixel, or else it is difficult to obtain aneffect. In this state, when the average value of the reset level issignificantly shifted, it may be a factor that prevents counting of acounter from being performed inaccurately and causes AD conversion to beappropriately performed.

Thus, there is a demand for a driving technique capable of spreading thereset level distribution without shifting the average value of the resetlevel.

The present technology was made in light of the foregoing, and it isdesirable to suppress deterioration of linearity in AD conversion and aquantization vertical streak caused by a quantization error with a highdegree of accuracy by driving while employing a technique of spreadingthe reset level distribution without shifting the average value of thereset level.

Solution to Problem

According to one aspect of the present technology, there is provided asolid-state imaging device including: a pixel section configured toinclude a plurality of pixels arranged in a matrix form, the pluralityof pixels performing photoelectric conversion; column signal linesconfigured to transmit pixel signals output from the pixels in units ofcolumns; an AD converting section configured to include a comparatorthat compares a reference signal serving as a ramp wave with the pixelsignals transmitted via the column signal line and convert a referencelevel and a signal level of the pixel signals into digital signalsindependently based on a comparison result of the comparator; a switchconfigured to be connected with the column signal lines; and a controlsection configured to turn on the switch only during a certain period oftime in a period of time in which the comparator is reset and cause thecolumn signal lines to be short-circuited.

The plurality of pixels may be arranged in the pixel section tocorrespond to a color filter in which colors are arranged in a certainrepetitive unit. The switch may be connected to each column signal lineof pixels of the same color.

The control section may adjust an ON period of time of the switchaccording to a gain of AD conversion performed by the AD convertingsection.

The control section may adjust a reset period of the comparatoraccording to the gain of the AD conversion performed by the ADconverting section.

The gain of the AD conversion performed by the AD converting section mayhave a value corresponding to the reference signal differing accordingto each color.

The switch may be a transistor. The transistor may include a gateconnected to the control section via a control line and a source and adrain that are connected to a row signal line connected to the columnsignal line in a row direction.

The switch may be a transistor. The transistor may include a gateconnected to the control section via a control line, a source connectedto the column signal line, and a drain connected to a row signal line ina row direction.

The switch may be connected with all the column signal lines.

The column signal lines may be divided into blocks in a certain unit.The switch may be connected with the column signal lines in units of theblocks.

The plurality of pixels arranged in the pixel section in the matrix formmay share at least an amplifying transistor and the column signal lineswith other pixels.

A noise adding section configured to add a noise that is temporallyunchanging and is irregular in a two-dimensional space to the pixelsignals transmitted via the column signal lines may be further included.

A driving method and an electronic device according to one aspect of thepresent technology are a driving method and an electronic devicecorresponding to the solid-state imaging device of one aspect of thepresent technology.

In a solid-state imaging device, a driving method, and an electronicdevice according to one aspect of the present technology, a referencelevel and a signal level of pixel signals transmitted via column signallines that transmit the pixel signals output from a pixel section inwhich a plurality of pixels performing photoelectric conversion arearranged in a matrix form are converted into digital signalsindependently based on a comparison result of a comparator that comparesa reference signal serving as a ramp wave with the pixel signals, and aswitch connected to the column signal lines is turned on only during acertain period of time in a period of time in which the comparator isreset, so that the column signal lines are short-circuited.

Advantageous Effects of Invention

According to one aspect of the present technology, it is possible tosuppress deterioration of linearity in AD conversion and a quantizationvertical streak caused by a quantization error with a high degree ofaccuracy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a CMOS image sensorof a related art.

FIG. 2 is a diagram illustrating a configuration and a connection formof a unit pixel.

FIG. 3 is a diagram illustrating a configuration of a comparator.

FIG. 4 is a diagram for describing driving in which a pulse width of apixel reset pulse RST is adjusted.

FIG. 5 is a diagram for describing driving in which a pulse width of acomparator reset pulse PSET is adjusted.

FIG. 6 is a diagram for describing a mechanism in which a reset levelaverage value is shifted.

FIG. 7 is a diagram schematically illustrating a reset leveldistribution when a reset level average value is shifted.

FIG. 8 is a diagram illustrating a configuration of a CMOS image sensoraccording to the present technology.

FIG. 9 is a diagram illustrating a configuration and a connection formof a switch.

FIG. 10 is a diagram for describing driving using a control pulseVSLCNT.

FIG. 11 is a diagram schematically illustrating a reset leveldistribution when a reset level average value is shifted.

FIG. 12 is a diagram for describing adjustment of a reset leveldistribution using a capacitive element.

FIG. 13 is a diagram for describing adjustment of a reset leveldistribution using a capacitive element.

FIG. 14 is a diagram illustrating a circuit for normal driving.

FIG. 15 is a timing chart for describing normal driving.

FIG. 16 is a diagram illustrating a circuit for driving according to thepresent technology.

FIG. 17 is a timing chart for describing driving according to thepresent technology.

FIG. 18 is a timing chart for describing driving according to thepresent technology.

FIG. 19 is a diagram illustrating comparative examples of imagesobtained as a result of AD conversion.

FIG. 20 is a diagram for describing driving performed in units of pixelsof the same color.

FIG. 21 is a diagram for describing driving in which an AD conversiongain is in conjunction with a control pulse VSLCNT.

FIG. 22 is a diagram for describing driving in which an AD conversiongain is in conjunction with an auto-zero period of time.

FIG. 23 is a diagram illustrating a configuration in which a referencesignal of each color is generated.

FIG. 24 is a diagram illustrating another example of a configuration anda connection form of a switch.

FIG. 25 is a diagram illustrating a configuration example of an imagingapparatus.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present technology will be describedwith reference to the appended drawings.

Here, in order to facilitate understanding of the present technology andclarify the background thereof, a configuration of a CMOS image sensorof a related art disclosed in Patent Literature 1 and a problem thereofwill be described with reference to FIGS. 1 to 7, and then a CMOS imagesensor according to the present technology will be described.

<CMOS Image Sensor of Related Art>

(Configuration of CMOS Image Sensor of Related Art)

FIG. 1 is a diagram illustrating a configuration of a CMOS image sensorof a related art.

As illustrated in FIG. 1, a CMOS image sensor 1 includes a pixel arraysection 11 formed on a semiconductor substrate (chip) and a peripheralcircuit section integrated on the same semiconductor substrate as thepixel array section 11. The peripheral circuit section includes avertical driving section 12, a read current source section 13, a columnprocessing section 14, a reference signal generating section 15, ahorizontal driving section 16, a communication timing control section17, an output section 18, and a noise adding section 19.

In the pixel array section 11, unit pixels 30 each including aphotoelectric conversion element that generates charges of a chargequantity according to an incident light quantity and accumulates thegenerated charges therein are two-dimensionally arranged in a matrixform.

In FIG. 1, for the sake of simplicity of description, some rows andcolumns are omitted, but in reality, many unit pixels 30 are arranged ineach row and each column. Typically, each of the unit pixels 30 includesa photodiode serving as a photoelectric conversion element and anin-pixel amplifier including an amplifying semiconductor device such asa transistor. For example, a floating diffusion amplifier is used as anin-pixel amplifier.

Further, in the pixel array section 11, row control lines 20 are formedin units of rows in a pixel array direction (a horizontal direction inFIG. 1) of a row of pixels with respect to the pixel array of the matrixform, and vertical signal lines 21 are formed in units of columns in apixel array direction (a vertical direction in FIG. 1) of a column ofpixels.

The vertical driving section 12 is configured with a shift register, anaddress decoder, and the like, and drives the pixels of the pixel arraysection 11 at the same time or in units of rows according to a controlsignal from the communication timing control section 17. A specificconfiguration of the vertical driving section 12 is not illustrated, butthe vertical driving section 12 is commonly configured to include twoscanning systems, that is, a read scanning system and a sweep scanningsystem.

Signals output from the unit pixels 30 of the pixel row selectivelyscanned by the vertical driving section 12 are supplied to the columnprocessing section 14 via the vertical signal lines 21. Further, thevertical signal line 21 has one end extending to the column processingsection 14 side, and the read current source section 13 is connected inthe path of the vertical signal line 21. The read current source section13 configures a source follower to which a substantially constantoperating current (a read current) is supplied together with theamplifying transistor of the unit pixel 30.

The column processing section 14 has an AD converting function ofconverting a reset level serving as a reference level of pixel signalstransmitted from the unit pixels 30 of a selected row via the verticalsignal line 21 and a signal level into digital signals independently foreach pixel column of the pixel array section 11 and a differentialprocessing function of acquiring a digital signal of a signal componentindicated by a difference between an AD conversion result of the resetlevel and an AD conversion result of the signal level.

Specifically, the pixel signal output from each unit pixel 30 is inputto a column AD converting section 41 of the column processing section 14via the vertical signal line 21. A reference signal generating section(digital analog converter (DAC)) 15 generates a reference signal RAMPhaving a ramp-like voltage according to the control signal from thecommunication timing control section 17, and supplies the referencesignal RAMP to each column AD converting section 41.

Then, when the reference signal RAMP is supplied from the referencesignal generating section 15, each column AD converting section 41starts counting in a clock signal at the same time at which thereference signal RAMP is supplied from the reference signal generatingsection 15. Then, each column AD converting section 41 compares theinput pixel signal with the reference signal RAMP, and performs countinguntil the input pixel signal is found to match the reference signal RAMPas a result of comparison, so that AD conversion is performed.

The details of the column processing section 14 and the reference signalgenerating section 15 will be described later.

The horizontal driving section 16 is configured with a shift register,an address decoder, and the like, and sequentially selects unit circuitsof the column processing section 14 corresponding to the pixel columnaccording to the control signal from the communication timing controlsection 17. Through the selective scanning function of the horizontaldriving section 16, a count value held in the column processing section14 is read out.

A horizontal signal line 22 includes a signal line of an n-bit widthcorresponding to a bit width of the column AD converting section 41, andis connected to the output section 18 via n sense circuits (notillustrated) corresponding to respective output lines (not illustrated).

The communication timing control section 17 is configured with a timinggenerator that generates a clock necessary for an operation of eachsection or a pulse signal of a certain timing or the like. Thecommunication timing control section 17 generates a clock or a pulsesignal based on a master clock (CLK) acquired from the outside or data(DATA) indicating an operation mode or the like, and performs drivingcontrol of the respective sections of the CMOS image sensor 1 such asthe vertical driving section 12, the column processing section 14, thereference signal generating section 15, and the horizontal drivingsection 16.

The noise adding section 19 adds a certain noise to a pixel signaltransmitted via the vertical signal line 21.

Specifically, the noise adding section 19 changes an on/off timing (forexample, a reset release timing of a comparator 44 which will bedescribed later) of a driving pulse for driving the unit pixel 30 and anAD conversion timing, and controls a bias current (a read current of theunit pixel 30) of the vertical signal line 21. Further, a noise signalthat does not change temporally but has a different noise levelaccording to a two-dimensional pixel position is included in the pixelsignal transmitted via the vertical signal line 21.

In other words, when a temporally changing noise is added to the pixelsignal, it is difficult to remove the noise, but a two-dimensionalspatial random noise that does not change temporally can be removed byperforming differential processing between the reset level and thesignal level in connection on the pixel signal at the same pixelposition. As described above, the noise adding section 19 can operate incollaboration with some functions of the column AD converting section41.

Through the above configuration, the pixel signals are sequentiallyoutput from the pixel array section 11 in units of rows for eachvertical column. Then, one image corresponding to the pixel arraysection 11 in which the photoelectric conversion elements are arrangedin a matrix form, that is, an image of one frame is obtained as a set ofpixel signals of the entire pixel array section 11.

(Detailed Configurations of Column Processing Section and ReferenceSignal Generating Section)

Here, detailed configurations of the column processing section 14 andthe reference signal generating section 15 of FIG. 1 will be described.

The reference signal generating section 15 generates a step-likesaw-tooth wave (a ramp waveform) based on the control signal from thecommunication timing control section 17. The reference signal generatingsection 15 supplies the generated saw-tooth wave to the column ADconverting sections 41 of the column processing section 14 as an ADconversion reference signal RAMP (an ADC reference voltage).

The control signal supplied from the communication timing controlsection 17 to the reference signal generating section 15 includesinformation for equalizing a change rate of a digital signal to time sothat ramp voltages of respective comparison processes have the sameinclination (change rate). Specifically, it is desirable to change acount value one by one for each unit time.

The column AD converting section 41 is disposed for each column of theunit pixels 30 configuring the pixel array section 11. Each of thecolumn AD converting sections 41 is configured with a capacitive element42, a capacitive element 43, the comparator 44, a counter 45, a switch46, and a memory 47.

One electrode of the capacitive element 42 is connected to the verticalsignal line 21 of the vertical column corresponding thereto in commonwith one electrode of the other capacitive element 42, and the pixelsignal from the unit pixel 30 is input to one electrode of onecapacitive element 42. Further, one input terminal of the comparator 44is connected to the other electrode of the capacitive element 42.

One electrode of the capacitive element 43 receives the reference signalRAMP from the reference signal generating section 15 in common with oneelectrode of the other capacitive element 43, and the other electrode ofthe capacitive element 43 is connected with the other input terminal ofthe comparator 44.

The capacitive elements 42 and 43 are used for signal coupling, and cut(DC-cut) a DC component of the signal input to the comparator 44.

One input terminal of the comparator 44 is connected with the otherelectrode of the capacitive element 42 and receives the DC-cut pixelsignal, and the other input terminal of the comparator 44 is connectedwith the other electrode of the capacitive element 43 and receives theDC-cut reference signal RAMP.

The comparator 44 compares the reference signal RAMP with the pixelsignals obtained from the unit pixels 30 via the vertical signal line 21(H0, H1, . . . , Hh) for each row control line 20 (V0, V1, . . . , Vv).An output terminal of the comparator 44 is connected to the counter 45,and the comparator 44 outputs a comparison processing result to thecounter 45.

The communication timing control section 17 has a function of switchinga mode of a count process in the counter 45 according to whether thecomparator 44 performs the comparison process on the reset level or thesignal of the pixel signal. Further, the count mode includes a downcount mode and an up count mode.

A count clock from the communication timing control section 17 is inputto a clock terminal of the counter 45 and a clock terminal of the othercounter 45 in common The counter 45 is configured to be able to switch adown-count operation and an up-count operation alternately using acommon up-down counter (U/D CNT) regardless of a count mode and performa count process.

The counter 45 has a latch function of holding a count result, and holdsthe counter value until an instruction is given through the controlsignal from the horizontal driving section 16.

Further, the n-bit memory 47 that holds the count value held in thecounter 45 and the switch 46 that performs a switching operationaccording to a counter value transfer instruction from the communicationtiming control section 17 are disposed behind the counter 45. The switch46 transfers the counter value of the counter 45 to the memory 47according to the transfer instruction from the communication timingcontrol section 17, and causes the counter value to be stored in thememory 47.

The memory 47 holds the count value acquired from the counter 45 untilan instruction is given through the control signal from the horizontaldriving section 16. The count value held in the memory 47 is read outthrough the horizontal driving section 16.

The column AD converting sections 41 having the above configuration isarranged for each vertical signal line 21 (H0, H1, . . . , Hh) asdescribed above, so that the column processing section 14 serving as anADC block of a column parallel configuration is configured. In thisconfiguration, the column AD converting section 41 performs the countoperation during a pixel signal read period of time corresponding to ahorizontal blanking period of time, and outputs a count result at acertain timing.

In other words, the comparator 44 compares a voltage level of thereference signal RAMP of a ramp waveform increasing or decreasing at acertain inclination with a voltage level of the pixel signal of thepixel signal from the unit pixel 30, and inverts its output when the twovoltage levels are equal to each other. Further, the counter 45 startsthe count operation in either the down-count mode or the up-count modein synchronization with the ramp waveform voltage output from thereference signal generating section 15, and when information that theoutput of the comparator 44 is inverted is notified of, the counter 45stops the count operation, and completes the AD conversion by holdingthe count value at that point in time.

Thereafter, the counter 45 sequentially outputs pixel data held thereinto the outside of the chip having the pixel array section 11 and thelike through the output section 18 and the like based on a shiftoperation by a horizontal selection signal input from the horizontaldriving section 16 at a certain timing.

In FIG. 1, for the sake of simplicity of description, for example,various kinds of circuits that do not relate directly to the descriptionof the present embodiment are not illustrated, but for example, thereare cases in which a signal processing circuit or the like is includedas a component of the CMOS image sensor 1.

The CMOS image sensor 1 of FIG. 1 has the above-described configuration.

(Configuration of Unit Pixel)

Next, a configuration example of the unit pixel 30 arranged in the pixelarray section 11 of the CMOS image sensor 1 of FIG. 1 and a connectionform between a driving control line and a pixel transistor will bedescribed with reference to FIG. 2.

As illustrated in FIG. 2, as a configuration of the unit pixel 30 in thepixel array section 11, for example, a 4 TR structure including fourtransistors may be employed.

The unit pixel 30 includes, for example, a diode 51 as a photoelectricconversion element, and includes four transistors, that is, a transfertransistor 52, a reset transistor 53, an amplifying transistor 54, and avertical selecting transistor 55 as active elements for one photodiode51. The unit pixel 30 further includes a pixel signal generating section57 of a floating diffusion amplifier configuration (floating diffusionAMP (FDA)) configured with a floating diffusion 56.

The photodiode 51 performs photoelectric conversion of convertingincident light into a quantity of charges according to a quantity oflight. The transfer transistor 52 is arranged between the photodiode 51and the floating diffusion 56.

As a driving pulse TRG is applied to a transfer gate from a transferdriving buffer 58 via a transfer line 59, the transfer transistor 52transfers the electrons obtained by the photoelectric conversion in thephotodiode 51 to the floating diffusion 56.

The floating diffusion 56 is connected with a gate of the amplifyingtransistor 54. The amplifying transistor 54 is connected to the verticalsignal line 21 via the vertical selecting transistor 55, and configuresthe source follower (the pixel source follower) together with the readcurrent source section 13 disposed outside the unit pixel 30.

When the unit pixel 30 is selected as a selection pixel from among anumber of unit pixels connected to the vertical signal line 21, avertical selection pulse VSEL is applied to a gate of the verticalselecting transistor 55 from a selective driving buffer 60 via avertical selection line 61, the vertical selecting transistor 55 isturned on, and the amplifying transistor 54 is connected with thevertical signal line 21. The amplifying transistor 54 amplifies apotential of the floating diffusion 56, and outputs a voltage accordingto the potential to the vertical signal line 21. A signal voltage outputfrom each pixel is output to the column processing section 14 as a pixelsignal (So) via the vertical signal line 21.

The reset transistor 53 is connected between a power line VRD and thefloating diffusion 56, and resets the potential of the floatingdiffusion 56 when a pixel reset pulse RST is applied from a resetdriving buffer 62 via a reset line 63.

More specifically, when the pixel is reset, the transfer transistor 52is turned on to discharge the charges remaining in the photodiode 51,and then the transfer transistor 52 is turned off, and the photodiode 51converts a light signal into charges and accumulates the charges.

At the time of reading, the reset transistor 53 is turned on to resetthe floating diffusion 56, the reset transistor 53 is then turned off,and the charges in the floating diffusion 56 at this time are outputthrough the amplifying transistor 54 and the vertical selectingtransistor 55. An output at this time is a reset level output (P phaseoutput).

Then, the transfer transistor 52 is turned on to transfer the chargesaccumulated in the photodiode 51, and the voltage of the floatingdiffusion 56 at this time is output through the amplifying transistor54. An output at this time is a signal level output (a D phase output).

Then, a difference between the signal level output (the D phase output)and the reset level output (the P phase output) is used as a pixelsignal, and thus it is possible to remove the reset noise of thefloating diffusion 56 from the pixel signal while preventing a variationin an output DC component of each pixel. For example, this operation isperformed simultaneously on the pixels of one row since the gates of thetransfer transistors 52, the vertical selecting transistors 55, and thereset transistor 53 are connected in units of rows.

The read current source section 13 includes an NMOS transistor 71(hereinafter, referred to as a “load NMOS transistor 71”) disposed ineach vertical column, a current generating section 72 shared by allvertical columns, and a reference power supply section 73 including anNMOS transistor 74. The source line 75 is connected to a ground servingas a substrate bias at an end portion in a vertical direction, and theoperating current (the read current) on the ground of the load NMOStransistor 71 is supplied from both left and right ends of the chip.

A drain of each load NMOS transistor 71 is connected to the verticalsignal line 21 of a corresponding column, a source thereof is connectedto the source line 75 serving as a grounding wire. Thus, the gate of theload NMOS transistor 71 of each vertical column is connected with a gateof a transistor 74 of the reference power supply section 73 to configurea current mirror circuit, and functions as a current source on thevertical signal line 21.

A load control signal SFLACT for outputting a certain current only whennecessary is supplied from a load control section (not illustrated) tothe current generating section 72. At the time of reading, the loadcontrol signal SFLACT of an active state is input to the currentgenerating section 72, and the current generating section 72 causes apredetermined current to continuously flow to each amplifying transistor54 through the load NMOS transistor 71 connected via the vertical signalline 21.

In other words, the load NMOS transistor 71 configures the sourcefollower with the amplifying transistor 54 of the selected row, suppliesthe read current to the amplifying transistor 54, and outputs the pixelsignal (So) to the vertical signal line 21.

(Configuration of Comparator)

Next, the details of the comparator 44 disposed in each column ADconverting section 41 of FIG. 1 will be described with reference to FIG.3.

The comparator 44 employs a different amplifier configuration as a basicconfiguration, and includes a differential transistor pair section 81, aload transistor pair section 82 serving as an output load of thedifferential transistor pair section 81, and a current source section83.

The differential transistor pair section 81 includes NMOS transistors 84and 85. The load transistor pair section 82 includes PMOS transistors 86and 87. The current source section 83 includes an NMOS constant currentsource transistor 88, and supplies a constant operating current to thedifferential transistor pair section 81 and the load transistor pairsection 82.

Sources of the transistors 84 and 85 are connected to a drain of aconstant current source transistor 86 of the current source section 83in common, and drains of the transistors 84 and 85 are connected todrains of the corresponding transistors 86 and 87 of the load transistorpair section 82. A DC gate voltage is input to a gate of the constantcurrent source transistor 88.

An output (the drain of the transistor 85 in the example of FIG. 3) ofthe differential transistor pair section 81 is connected to an amplifier(not illustrated), passes through a buffer (not illustrated), and issufficiently amplified and then output to the counter 45 (FIG. 1).

Further, an operation point reset section 91 that resets an operationpoint of the comparator 44 is disposed. The operation point resetsection 91 functions as an offset removing section. In other words, thecomparator 44 is configured as a voltage comparator with an offsetremoving function. The operation point reset section 91 includesswitching transistors 92 and 93.

The switching transistor 92 is connected between the gate and the drainof the transistor 84. The switching transistor 93 is connected betweenthe gate and the drain of the transistor 85. A comparator reset pulsePSET is supplied to gates of the switching transistors 92 and 93 incommon.

The pixel signal is input to the gate of the transistor 84 via thecapacitive element 42 (FIG. 1) for signal coupling. Further, the pixelsignal is input to the gate of the transistor 85 via the capacitiveelement 43 (FIG. 1) for signal coupling.

In the above configuration, the operation point reset section 91performs a sample/hold function on signals input through the capacitiveelements 42 and 43.

In other words, the comparator reset pulse PSET becomes active (forexample, an H level) only immediately before a comparison of the pixelsignal and the reference signal RAMP starts, and the operation point ofthe differential transistor pair section 81 is reset to a drain voltage(a read potential; an operation reference value for reading a referencecomponent or a signal component).

Thereafter, the pixel signal is input to the transistor 84 via thecapacitive element 42, the reference signal RAMP is input to thetransistor 85 via the capacitive element 43, and the comparison isperformed until the pixel signal and the reference signal RAMP becomethe same potential. Then, when the pixel signal and the reference signalRAMP become the same potential, the output is inverted.

In the following description, a state in which the comparator resetpulse PSET becomes active is also referred to as an “auto zero (AZ).”

Further, for the sake of convenience of description, the capacitiveelements 42 and 43 of FIG. 1 have been described as being disposedoutside the comparator 44, but the capacitive elements 42 and 43 may bedisposed in the comparator 44 of FIG. 3 and configured as a part of theoperation point reset section 91. In this case, the capacitive element42 is arranged between the input terminal to which the pixel signal isinput and the gate of the transistor 84, and the capacitive element 43is arranged between the input terminal to which the reference signalRAMP is input and the gate of the transistor 85. Further, the input ofthe pixel signal and the input of the reference signal RAMP may bereversed.

(Problem of AD Conversion in CMOS Sensor of Related Art)

Meanwhile, in the CMOS image sensor 1, when the AD conversion isperformed, the concentration of the energy is prevented, or the verticalstreak caused by the quantization error is suppressed such that theoperation period of time of the column AD converting section 41 isvaried by injecting a certain noise through the noise adding section 19or the like and spreading the reset level distribution, but a phenomenonin which the average value of the reset level is shifted at the sametime at which the reset level distribution is spread occurs.

The reason for which this phenomenon occurs was found through a detailedsimulation performed by the inventor(s) of the present technology. Inthis regard, the details of a mechanism in which the average value ofthe reset level is shifted will be described below with reference toFIGS. 4 to 7.

Here, in normal reading and AD conversion of the pixel signal, after thereset level appearing on the vertical signal line 21 is sufficientlystabilized, and then the AD conversion is performed on the reset level.On the other hand, in the CMOS image sensor 1, the AD conversion isperformed on the reset level before the reset level appearing on thevertical signal line 21 is stabilized, and thus the AD conversion isperformed on the reset level of an unstable state.

This means that the reset noise is mixed into the AD conversion result,but since the amount of the reset noise differs according to each pixel,a mixing state differs according to each pixel as well, and atwo-dimensionally irregular noise is consequently mixed into the ADconversion result of the reset level.

Further, as a technique of performing AD conversion on the reset levelof the unstable state, Patent Literature 1 discloses a technique ofadjusting an interval (hereinafter, a “reset release interval TRelease”)between a timing at which the pixel reset pulse RST is turned off and atiming at which the comparator reset pulse PSET for resetting thecomparator 44 is turned off so that the interval is smaller than agenerally employed interval.

In other words, as illustrated in FIG. 4, by shifting a timing at whichthe pixel reset pulse RST is turned off to a later timing and reducingthe reset release interval TRelease, the reset state of the comparator44 is purposely released at a timing at which the reset noise isunstable. Thus, an irregular noise can be injected into the ADconversion result of the reset level.

Similarly, as illustrated in FIG. 5, by shifting a timing at which thecomparator reset pulse PSET is turned off to a previous timing andreducing the reset release interval TRelease, an irregular noise can beinjected into the AD conversion result of the reset level.

As described above, in the CMOS image sensor 1, by performing signalsampling in the middle of a settling period of time to the inputcapacitance of the comparator 44, the irregular noise is injected intothe AD conversion result of the reset level, and the reset leveldistribution is spread.

Specifically, as illustrated in a timing chart of FIG. 6, according to anormal driving timing, as indicated by a dotted line in FIG. 6, afterthe pixel reset pulse RST is input and then a reset noise componentappearing on the vertical signal line 21 is stabilized, the comparatorreset pulse PSET for the comparator 44 is turned off, and thus theoffset component of the pixel signal (So) is completely removed.

On the other hand, according to a driving timing of the CMOS imagesensor 1, as indicated by a solid line, when a noise component isinjected, a timing at which the pixel reset pulse RST is turned off ispurposely shifted to a later timing, and thus the reset release interval(TRelease) is reduced. As a result, the reset state of the comparator 44is purposely released at a timing at which the reset noise is unstable.This means that a two-dimensionally irregular noise is injected bycontrolling the pulse width of the pixel reset pulse RST for pixel resetand a settling amount of the reset noise of the pixel.

As a result, the unstable reset noise component is mixed into the ADconversion result of the reset level, but since the amount of the resetnoise differs according to each pixel as described above, mixing statesare various, and a two-dimensionally irregular noise can be consequentlymixed into the AD conversion result of the reset level.

Further, since there is a time from the reset release of the comparator44 to the actual slope start of the reference signal RAMP (that is, theAD conversion start), this period of time is set to an operation timingin which the reset noise component of the vertical signal line 21 iscompletely stable, and thus the reset level does not vary between thetime of AD conversion on the subsequent reset level and the time of ADconversion on the signal level. Thus, a noise component that istemporally random is not included, and image quality does notdeteriorate.

In other words, practically, a two-dimensionally irregular fixed patternnoise of the same amount is injected into the reset level and the signallevel of the pixel signal, AD conversion is performed, and thedifferential process is performed on each AD conversion result, and thusthe digital signal of the signal component is acquired in a state inwhich a quantization noise generated in association with thedifferential process becomes random in a two-dimensional space.

As described above, the CMOS image sensor 1 operates according to thedriving timing of FIG. 6 and spreads the reset level distribution, andthus the CMOS image sensor 1 prevents concentration of energy, preventsa phenomenon in which a quantization error occurring in association withthe differential process is accumulated for each column, and suppressesan unnatural noise of a vertical streak form.

However, in the case of the driving timing of FIG. 6, since signalsampling is performed in the middle of the settling period of time, thereset level distribution is not spread, and the phenomenon in which theaverage value of the reset level is shifted occurs.

FIG. 7 is a diagram schematically illustrating the reset leveldistribution when the average value of the reset level is shifted.

In FIG. 7, a horizontal axis denotes a reset level output value, and avertical axis denotes the frequency thereof Further, in FIG. 7, drivingaccording to a driving timing indicated by a dotted line in FIG. 6 isreferred to as “normal driving,” and driving according to a drivingtiming indicated by a solid line in FIG. 6 is referred to as “ditherdriving.”

In the normal driving, since noise injection is not performed, asindicated by a dotted line in FIG. 7, the reset level distribution doesnot flare but is concentrated near the average value. Further, sincenoise injection is not performed, the reset level output value does notbecome as large. Thus, the reset level output value does not exceed amaximum reset level count value.

On the other hand, in the dither driving, since noise injection isperformed through the noise adding section 19 or the like, the resetlevel distribution is spread, but as noise is injected, the reset leveloutput value increases accordingly, and thus the average value isshifted to the right in FIG. 7 compared to the case of the normaldriving. Thus, a case in which the reset level output value exceeds themaximum reset level count value occurs.

As described above, when the average value of the reset level issignificantly shifted so that the reset level output value exceeds themaximum value in which the reset level can be counted, accurate countingby the counter 45 may not be performed, and the AD conversion may not beappropriately performed. In order to prevent this phenomenon, it isnecessary to suppress the shift of the average value of the reset level,but the inventor of the present technology has found a technique ofsuppressing the shift of the average value of the reset level. In thisregard, the CMOS image sensor according to the present technology willbe described below.

<CMOS Image Sensor According to Present Technology>

(Configuration Example of CMOS Image Sensor According to PresentTechnology)

FIG. 8 is a diagram illustrating a configuration example of a CMOS imagesensor as a solid-state imaging device according to the presenttechnology.

In a CMOS image sensor 101 of FIG. 8, parts corresponding to those ofthe CMOS image sensor 1 of FIG. 1 are denoted by the same referencenumerals, and a description thereof will be appropriately omitted.

In other words, the CMOS image sensor 101 differs from the CMOS imagesensor 1 in that a switch 110 is disposed between the pixel arraysection 11 and the read current source section 13.

The switch 110 is connected to the vertical signal lines 21. The switch110 causes the vertical signal lines 21 to be short-circuited accordingto a control pulse VSLCNT input from the communication timing controlsection 17 via a control line 23. Then, when the vertical signal lines21 are short-circuited, a potential of each vertical signal line 21becomes an average potential, and this is stored, and thus the shift ofthe average value of the reset level can be suppressed.

Here, a technique of suppressing the shift of the average value of thereset level will be described in further detail with reference to FIGS.9 to 13.

In FIG. 9, for the sake of convenience of description, among the unitpixels 30 arranged in a matrix form in the pixel array section 11, aunit pixel 30-1 and a unit pixel 30-2 are illustrated. In FIG. 9, partscorresponding to those of FIG. 2 are denoted by the same referencenumerals, and a description thereof will be omitted.

In the unit pixel 30-1, an amplifying transistor 54-1 is connected witha vertical signal line 21-1 via a vertical selecting transistor 55-1,and configures the source follower together with a read current sourcesection 13-1. In FIG. 9 and the like, an output of the source followeris indicated by “VSL1.”

A column AD converting section 41-1 is connected to the vertical signalline 21-1. In the column AD converting section 41-1, the pixel signalfrom the unit pixel 30-1 is input to one input terminal of a comparator44-1 via a capacitive element 42-1, and a reference signal RAMP from areference signal generating section 15 is input to the other inputterminal of the comparator 44-1 via a capacitive element 43-1. In FIG. 9and the like, an output of the capacitive element 42-1 is indicated by“VSL1D.”

Similarly, in the unit pixel 30-2, an amplifying transistor 54-2 and aread current source section 13-2 configure the source follower. A columnAD converting section 41-2 is connected to a vertical signal line 21-2.In FIG. 9 and the like, an output of the source follower is indicated by“VSL2,” and an output of a capacitive element 42-2 is indicated by“VSL2D.”

The switch 110 is configured with a switching transistor 111. A sourceof the switching transistor 111 is connected with the vertical signalline 21-1 via a row signal line 112, and a drain of the switchingtransistor 111 is connected with the vertical signal line 21-2 via therow signal line 112. In other words, the switching transistor 111connects the outputs of the source followers configured for each columnby connecting the vertical signal lines 21 in the row direction throughthe row signal line 112.

A control pulse VSLCNT from the communication timing control section 17is input to a gate of the switching transistor 111. Thus, the switchingtransistor 111 performs an on/off switching operation according to thecontrol pulse VSLCNT from the communication timing control section 17.

For example, as illustrated in FIG. 10, the control pulse VSLCNT has theH level only during a certain period of time in a period of time inwhich the comparator reset pulse PSET on the comparator 44 is in theactive state. Further, when the control pulse VSLCNT input to the gatebecomes the H level, the switching transistor 111 enters the on state,and causes the vertical signal lines 21 connected to the row signal line112 to be short-circuited. When the vertical signal lines 21 areshort-circuited, the potential of each vertical signal line 21 becomesthe average potential, and an output of the source follower of eachcolumn becomes an averaged output. For example, in FIG. 9, the outputsVSL1 and VSL2 of the source followers are averaged.

As a result, an average value of the outputs of the source followers isstored in one input terminal of the comparator 44 arranged in eachcolumn AD converting section 41 as the input capacitance.

Thereafter, when the control pulse VSLCNT input to the gate reaches theL level, the switching transistor 111 enters the off state, and returnsthe vertical signal lines 21 connected to the row signal line 112 to anoriginal state before it was short-circuited. As a result, the output ofeach source follower of each column is returned from the average valueto the output value according to a variation of a threshold voltage(Vth) of each amplifying transistor 54.

At this time, a pixel signal corresponding to the variation of thethreshold voltage of each amplifying transistor 54 from the averagevalue of the outputs of the source followers stored during the period oftime (the auto zero period of time) in which the comparator reset pulsePSET is in the active state is input to one input terminal of thecomparator 44. Thus, the output of the comparator 44 arranged in eachcolumn AD converting section 41 is distributed according to thevariation of threshold voltage of each amplifying transistor 5.

Further, since the output distribution is spread centering on theaverage value of the outputs of the source followers, it is possible tospread the reset level distribution without the occurrence of the shiftof the average value of the reset level described above. In other words,since the vertical signal lines 21 are short-circuited by the switchingtransistor 111, a noise is added to the pixel signal transmitted via thevertical signal line 21.

FIG. 11 is a diagram schematically illustrating the reset leveldistribution when the shift of the average value of the reset level doesnot occur.

In the dither driving of FIG. 11, similarly to the dither driving ofFIG. 7, the reset level distribution is spread, but since the resetlevel distribution is spread centering on the average value of theoutputs of the source followers, the average value of the reset level isnot shifted compared to the case of the normal driving. Thus, the resetlevel output value does not exceed the maximum reset level count value,and the counter 45 can perform accurate counting. As a result, the ADconversion is appropriately performed, and the distribution is spread.Thus, concentration of energy is mitigated, and it is possible tosuppress deterioration of linearity caused by power fluctuation and aquantization vertical streak caused by a quantization error with a highdegree of accuracy.

The reset level distribution is flared using the characteristics of thecapacitive element 42 for signal coupling. FIGS. 12 and 13 illustratespecific examples of the DC cut in the capacitive elements 42-1 and 42-2(FIG. 9) in the auto zero period of time (the AZ period of time) and thereset level period of time and the reset level distribution at thatpoint in time.

A of FIG. 12 illustrates a voltage value of the DC cut in the case ofthe normal driving and the reset level distribution at that point intime for a comparison with B of FIG. 12. In this case, since the outputsof the source followers of the respective columns are not averaged,input voltages of the capacitive elements 42-1 and 42-2 in the auto zeroperiod of time are 1.0 V and 2.0 V, and output voltages become 1.8 Vthrough the DC cut.

Thereafter, in the reset level period of time, the input voltages of thecapacitive elements 42-1 and 42-2 are 1.0 V and 2.0 V, respectively, andoutput voltages become 1.8 V through the DC cut. Further, in the normaldriving, the reset level distribution in the reset level period of timeis hardly spread, similarly to the auto zero period of time, and doesnot flare.

B of FIG. 12 illustrates the voltage value of the DC cut when driving isperformed according to the driving timing illustrated in FIG. 10 and thereset level distribution at that point in time. In this case, theswitching transistor 111 enters the on state, and the outputs of thesource followers of the respective columns are averaged, and thus theinput voltages of the capacitive elements 42-1 and 42-2 in the auto zeroperiod of time become 1.5 V. Then, the DC cut is performed through thecapacitive elements 42-1 and 42-2, and thus both of the output voltagesbecome 1.8 V.

Thereafter, the switching transistor 111 enters the off state, and thevertical signal lines 21-1 and 21-2 are returned to the original state,and thus the input voltages of the capacitive elements 42-1 and 42-2 inthe reset level period of time become 1.0 V and 2.0 V, respectively.Then, when the DC cut is performed through the capacitive elements 42-1and 42-2, the output voltages become 1.3 V and 2.3 V according to thecharacteristics of the capacitive elements 42.

Then, as illustrated in B of FIG. 12, in the auto zero period of time,the input voltages become 1.5 which is the average value of the outputsof the source followers, and in the subsequent reset level period oftime, when 1.0 V and 2.0 V are input as the input voltage, the outputvoltages are varied to 1.3 V and 2.3 V, and thus the reset leveldistribution in the reset level period of time has the increased width.

As described above, in the driving of B of FIG. 12 according to thepresent technology, the width of the reset level distribution can beincreased to be larger than that in the normal driving of A of FIG. 12.

Next, a specific example of FIG. 13 will be described. A of FIG. 13 isillustrated for a comparison with B of FIG. 13 and is the same as A ofFIG. 12, and thus a description thereof is omitted.

B of FIG. 13 illustrates the voltage value of the DC cut when driving isperformed according to the driving timing illustrated in FIG. 10 and thereset level distribution at that point in time. In B of FIG. 13, theswitching transistor 111 enters the on state, but enters the off statebefore the outputs of the source followers of the respective columns arecompletely averaged, and thus in the auto zero period of time, the inputvoltages of the capacitive elements 42-1 and 42-2 do not become onevalue but become 1.2 V and 1.8 V. Then, the DC cut is performed throughthe capacitive elements 42-1 and 42-2, and thus both of the outputvoltages become 1.8 V.

Thereafter, in the reset level period of time, the input voltages of thecapacitive elements 42-1 and 42-2 become 1.0 V and 2.0 V, respectively.Then, when the DC cut is performed through the capacitive elements 42-1and 42-2, the output voltages become 1.6 V and 2.0 V, respectively.

Then, as illustrated in B of FIG. 13, in the auto zero period of time,the input voltages get closer to the average value (for example, 1.5 V)of the outputs of the source followers such as 1.2 V and 1.8 V, and inthe subsequent reset level period of time, when 1.0 V and 2.0 V areinput as the input voltages, the output voltages are varied to 1.6 V and2.0 V, and thus the reset level distribution in the reset level periodof time has the increased width.

The reset level distribution in the reset level period of time of B ofFIG. 13 has the width smaller than the reset level distribution in thereset level period of time of B of FIG. 12 since the input voltages arenot completely averaged, but as the distribution is widened, the noisecan be injected accordingly.

As described above, in the driving of B of FIG. 13 according to thepresent technology, the reset level distribution has the larger widththan in the normal driving of A of FIG. 13.

<Driving According to Present Technology>

Next, the driving according to the present technology will be describedin further detail. Here, in order to facilitate understanding of thepresent technology and clarify the background thereof, the normaldriving will be described with reference to FIGS. 14 and 15, and thenthe driving according to the present technology will be described.

(Normal Driving)

FIG. 14 is a diagram illustrating a driving circuit used in the normaldriving.

As illustrated in FIG. 14, in the normal driving, since the outputs ofthe source followers of the respective columns are not averaged, the rowsignal line 112 is not connected to the vertical signal lines 21-1 and21-2, and the switching transistor 111 is not disposed. Thus, the normaldriving is performed as illustrated in a timing chart of FIG. 15.

In other words, at a time t11, when the comparator reset pulse PSET isturned on at the same time at which the pixel reset pulse RST is turnedon, the voltage values of the outputs VSL1 and VSL2 of the sourcefollowers start to increase, and continuously increase until the pixelreset pulse RST is turned off at a time t12. Further, when a time t12has elapsed, in the auto zero period of time, the voltage values of theoutputs VSL1 and VSL2 of the source followers decrease and become 2.0 Vand 1.0 V, respectively.

Thereafter, in the reset level period of time from a time t13 to a timet14, the ON period of time of the driving pulse TRG from the time t14 toa time t15, and the signal level period of time after the time t15, theoutputs VSL1 and VSL2 become constant voltage values of 2.0 V and 1.0 V,respectively.

Further, since the outputs VSL1D and VSL2D of the capacitive elements 42are DC-cut through the capacitive elements 42 as described above withreference to A of FIG. 12 and A of FIG. 13, the outputs VSL1D and VSL2Dof the capacitive elements 42 become 1.8 V serving as the voltage valueafter the DC cut in all the periods of time.

The normal driving has been described above.

(Driving According to Present Technology)

FIG. 16 is a diagram illustrating a driving circuit used in the drivingaccording to the present technology.

As illustrated in FIG. 16, in the driving according to the presenttechnology, since the outputs of the source followers of the respectivecolumns are averaged, the row signal line 112 is connected to thevertical signal lines 21-1 and 21-2, and the switching transistor 111 isfurther disposed. Thus, the driving according to the present technologyis performed as illustrated in a timing chart of FIG. 17 or FIG. 18.

As illustrated in FIG. 17, at a time t21, when the comparator resetpulse PSET is turned on at the same time at which the pixel reset pulseRST is turned on, the voltage values of the outputs VSL1 and VSL2 of thesource followers start to increase, and continuously increase until thepixel reset pulse RST is turned off at a time t22. Similarly, thevoltage values of the outputs VSL1D and VSL2D of the capacitive elements42 continuously increase from the time t21 to the time t22.

Further, when the time t22 has elapsed, in the auto zero period of time,the voltage values of the outputs VSL1 and VSL2 of the source followersdecrease. Then, when the control pulse VSLCNT is turned on at a timet23, the vertical signal lines 21 are short-circuited through theswitching transistor 111, and the outputs of the source followers of therespective columns are averaged. As a result, at a time t24, the outputsVSL1 and VSL2 become an average value, that is 1.5 V. In other words,the vertical signal lines 21 are short-circuited through cross coupling,and thus the outputs of the source followers are averaged.

Further, since the outputs VSL1D and VSL2D of the capacitive elements 42are DC-cut through the capacitive elements 42 as described above withreference to B of FIG. 12, at the time t24, the outputs VSL1D and VSL2Dbecome 1.8 V serving as the voltage value after the DC cut.

Thereafter, after the time t24, the control pulse VSLCNT is turned off,the vertical signal lines 21 are returned to the original state beforethey were short-circuited, and thus in the reset level period of time,the voltage values of the outputs VSL1 and VSL2 of the source followersbecome 2.0 V and 1.0 V, respectively. Then, in the ON period of time ofthe driving pulse TRG from a time t25 to a time t26 and the signal levelperiod of time after the time t26, the outputs VSL1 and VSL2 becomeconstant voltage values of 2.0 V and 1.0 V, respectively.

Further, when the outputs VSL1D and VSL2D of the capacitive elements 42are DC-cut through the capacitive elements 42 as described above withreference to B of FIG. 12, the outputs VSL1D and VSL2D become 2.3 V and1.3 V according to characteristics thereof In other words, when thecontrol pulse VSLCNT is turned off, the outputs of the source followersmove, and thus the nodes after the DC cut follow the outputs of thesource followers, and the reset level distribution is spread. As aresult, the noise is added to the pixel signal transmitted via thevertical signal line 21.

Further, as described above, when the switching transistor 111 entersthe on state, although the switching transistor 111 enters the on statebefore the outputs of the source followers of the respective columns arecompletely averaged, it is possible to spread the reset leveldistribution and add the noise. For example, as illustrated in FIG. 18,when the control pulse VSLCNT is turned on at a time t33, but at a timet34 that is temporally earlier than a timing at which the outputs of thesource followers of the respective columns are completely averaged, thecontrol pulse VSLCNT is turned on, and thus the outputs VSL1 and VSL2become 1.8 V and 1.2 V, respectively.

Thereafter, after the time t34, the control pulse VSLCNT is turned on,and the vertical signal lines 21 are returned to the original statebefore they were short-circuited, and thus in the reset level period oftime, the voltage values of the outputs VSL1 and VSL2 of the sourcefollowers become 2.0 V and 1.0 V, respectively. Further, in the ONperiod of time of the driving pulse TRG from a time t35 to a time t36and the signal level period of time after the time t36, the outputs VSL1and VSL2 become constant voltage values of 2.0 V and 1.0 V,respectively.

In other words, as the vertical signal lines 21 are cross-coupled, theoutputs VSL1 and VSL2 are averaged, but even when the pulse width of thecontrol pulse VSLCNT is reduced, and the cross-coupling is disconnectedin the middle, it is possible to inject the noise according to a changein the outputs of the source followers.

Further, because the outputs VSL1D and VSL2D of the capacitive elements42 are DC-cut through the capacitive elements 42 as described above withreference to B of FIG. 13, at the time t34, the outputs VSL1D and VSL2Dbecome 1.8 V serving as the voltage value after the DC cut. Thereafter,after the time t34, the outputs VSL1D and VSL2D become 2.0 V and 1.6 Vaccording to the characteristics of the capacitive element 42.

In other words, this is not the case in which, when the control pulseVSLCNT is turned off, the outputs of the source followers move, and thusthe nodes after the DC cut follow the outputs of the source followers,and the outputs of the source followers are completely averaged, but thereset level distribution is spread. In other words, it is possible toadjust the width of the reset level distribution according to the pulsewidth of the control pulse VSLCNT.

As described above, in the driving of FIGS. 17 and 18 according to thepresent technology, it is possible to increase the width of the resetlevel distribution to be larger than that in the normal driving of FIG.15.

Further, for the sake of simplicity of description, the timing charts ofFIGS. 15, 17, and 18 are based on an example in which a black signal inwhich light is not incident on the photodiode 51 is read. In otherwords, when light is incident, if the driving pulse TRG is turned on,the charges accumulated in the photodiode 51 are transferred to thefloating diffusion 56, so that the signal level is read, and the valuesof the outputs VSL1 and VSL2 of the source followers are changed.

The driving according to the present technology has been describedabove.

According to the driving according to the present technology, when thenoise is injected in order to suppress concentration of energy, aquantization vertical streak, and the like, the shift of the averagevalue of the reset level does not occur, and the reset leveldistribution can be spread. As a result, since the AD conversion isappropriately performed, it is possible to suppress deterioration oflinearity in AD conversion and a quantization vertical streak caused bya quantization error with a high degree of accuracy.

For example, as illustrated in A of FIG. 19, in the case of the normaldriving, a quantization error is accumulated in the result obtained byperforming the differential process between the AD conversion result ofthe reset level and the AD conversion result of the signal level eachtime, and a vertical streak-like noise caused by the quantization erroris found in an image obtained as a result.

On the other hand, in the case of the driving according to the presenttechnology, since the noise is injected, a quantization error isgenerated irregularly for each pixel, and the quantization error is notaccumulated for each column. Thus, since the image obtained byperforming the differential process is an image in which thequantization error is interposed similarly to A of FIG. 19, thequantization errors are irregularly distributed, and thus a verticalstreak form is not recognized at all as illustrated in B of FIG. 19.

As described above, it is possible to reduce the vertical streak noisecaused by the quantization noise after the differential process only byinjecting the noise into the reset level serving as the reference of thedifferential process. In A of FIG. 19 and B of FIG. 19, the amount ofnoise remaining even after the differential process does not change, butwhen the noise is accumulated for each column and recognized as thevertical streak noise, human perception is significantly different fromwhen the noise is irregularly distributed, and when the noise isirregularly distributed, it is more naturally accepted. It is due tohumans' cognitive psychological characteristics that consciousnessconcentrates on a geometric pattern when geometric pattern recognitionis possible.

Further, in the shift of the average value of the reset level,performing an offset adjustment may be considered, but in order toimplement this, an offset gain linkage or automatic adjustment functionis necessary, and thus the circuit size is increased. In the presenttechnology, since it is possible to suppress the shift of the averagevalue of the reset level only by installing the switching transistor111, the circuit size is not increased.

Further, in the present technology, the vertical signal lines 21 areshort-circuited, so that the noise is added to the pixel signaltransmitted via the vertical signal line 21, but as illustrated in FIG.8, a noise that is temporally unchanging but is irregular in atwo-dimensional space may be added through the noise adding section 19.

Another Embodiment

(Driving for each Pixel of Same Color)

Meanwhile, in the CMOS image sensor 101 of FIG. 8, the unit pixels 30arranged in the pixel array section 11 correspond to color imaging. Inother words, in a plurality of unit pixels 30 that are arranged in thepixel array section 11 in the matrix form, any one color filter of acolor separation filter including a combination of color filters of aplurality of colors for imaging a color image is disposed on a lightreception plane of each photodiode 51 on which light is incident.

In the example illustrated in FIG. 20, a color filter of a basic form ofa so-called Bayer array (a Bayer arrangement) is used, and the pixelarray section 11 is configured such that the unit pixels 30two-dimensionally arranged in the matrix form correspond to three colorfilters of red (R), green (G), and blue (B), and repetitive units of thecolor separation filter are arranged in the form of 2×2 pixels.

For example, a first color pixel for detecting a first color (forexample, R) is arranged at a position of an odd-numbered row and anodd-numbered column, a second color pixel for detecting a second color(for example, G) is arranged at a position of an odd-numbered row and aneven-numbered column and a position of an even-numbered row and anodd-numbered column, and a third color pixel for detecting a third color(for example, B) is arranged at a position of an even-numbered row andan even-numbered column. In other words, colors pixels of two colors ofR/G or G/B differing according to each row are arranged in acheckerboard pattern form.

In the color array of the color filters of the basic form of the Bayerarray, two colors of R/G or G/B are repeated two by two in both the rowdirection and the column direction, but a configuration in which theswitching transistor 111 is disposed for each color of a color pixel,the vertical signal lines 21 are connected by the row signal line 112for each color, and the outputs of the source followers of the samecolor are combined may be provided.

For example, in FIG. 20, the vertical signal lines 21 of theeven-numbered columns to which color pixels of the even-numbered column(R or G) are connected are connected by a row signal line 112-1, and theoutputs of the source followers thereof are connected. Similarly, thevertical signal lines 21 of the odd-numbered columns to which colorpixels of the odd -numbered column (G or B) are connected are connectedby a row signal line 112-2, and the outputs of the source followersthereof are connected.

A switching transistor 111-1 in which the control pulse VSLCNT is inputto a gate thereof is disposed in the row signal line 112-1 connectingthe vertical signal lines 21 of the even-numbered columns for eachcolor. Further, a switching transistor 111-1 in which the control pulseVSLCNT is input to a gate thereof is disposed in the row signal line112-2 connecting the vertical signal lines 21 of the odd-numberedcolumns for each color.

Further, as the switching transistors 111-1 and 112-2 perform aswitching operation according to the control pulse VSLCNT, the verticalsignal lines 21 of the even-numbered columns or the odd-numbered columnscan be short-circuited, and the outputs of the source followers can beaveraged for each color.

Here, it is commonly known that neighboring color pixels of the samecolor output signals of the same level, and color pixels of differentcolors output signals of different levels. In other words, since theoutputs of the source followers of the same color are signals of thesame level, it is possible to spread the distribution using the averagevalue of the reset level of each color by causing the connected verticalsignal lines 21 of the same color to be short-circuited, and thus it ispossible to prevent concentration of energy with a high degree ofaccuracy.

(Linkage of AD Conversion Gain and Control Pulse VSLCNT)

In the CMOS image sensor 101 of FIG. 8, the AD conversion gain isadjusted by changing the inclination of the slope of the referencesignal RAMP generated by the reference signal generating section 15.Specifically, as the inclination of the reference signal RAMP isgentler, a point in time at which the reference signal RAMP matches thepixel signal transmitted via the vertical signal line 21 is delayedmore, and thus a large digital signal is obtained, and the AD conversiongain is increased. Adversely, when the inclination of the referencesignal RAMP is steeper, the AD conversion gain is decreased.

In other words, a point in time at which the reference signal RAMPmatches the pixel signal transmitted via the vertical signal line 21 isadjusted by changing the inclination of the reference signal RAMP. As aresult, even when the signal voltages of the pixel signals transmittedvia the vertical signal lines 21 are the same, a count value at amatching point in time, that is, the digital signal of the signalvoltage, is adjusted. This means that the changing of the inclination ofthe reference signal RAMP is equivalent to the adjusting of the ADconversion gain.

Here, for example, when the inclination of the reference signal RAMP ishalved, and the AD conversion gain is doubled, the inclination when thereset level is acquired becomes ½, and thus when the distribution is thesame as before the inclination was halved, it deviates from the range ofthe reference signal RAMP, and it is difficult to acquire the resetlevel.

Thus, when the AD conversion gain is set to be high, it is necessary tonarrow the reset level distribution, and when the AD conversion gain isset to be low, it is necessary to widen the reset level distribution,but since it is possible to adjust the width of the reset leveldistribution according to the pulse width of the control pulse VSLCNT asdescribed above, this can be used herein.

In other words, as illustrated in FIG. 21, the control pulse VSLCNT isat the H level only during a certain period of time in the period oftime (the auto zero period of time) in which the comparator reset pulsePSET on the comparator 44 is the active state, but the period of time ofthe H level is adjusted according to the AD conversion gain.Specifically, when the AD conversion gain is set to be high, the pulsewidth of the control pulse VSLCNT is reduced so that the reset leveldistribution is not widened. On the other hand, when the AD conversiongain is set to be low, the pulse width of the control pulse VSLCNT isincreased so that the reset level distribution is widened.

As a result, for example, when the AD conversion gain is set to be low,if the pulse width of the control pulse VSLCNT is increased, the resetlevel distribution is widened, and the distribution thereof is spread,and thus it is possible to prevent concentration of energy with a highdegree of accuracy.

(Linkage of AD Conversion Gain and Auto Zero Period of Time)

Further, it is possible to adjust the pulse width of the comparatorreset pulse PSET in conjunction with the AD conversion gain.

For example, when the inclination of the reference signal RAMP is gentleand the AD conversion gain is low, in order to prevent the quantizationerror, the pulse width of the comparator reset pulse PSET is decreasedso that the rising edge of the comparator reset pulse PSET gets closerto the rising edge of the pixel reset pulse RST as indicated by a solidline in FIG. 22. In other words, by decreasing the reset releaseinterval TRelease, the comparator 44 is turned off by the comparatorreset pulse PSET before the reset noise appearing on the vertical signalline 21 is stabilized, and thus the reset noise is actively injected.

On the other hand, when the inclination of the reference signal RAMP issteep and the AD conversion gain is high, a priority is given tostabilization of the AD conversion, and the pulse width of thecomparator reset pulse PSET is widened as indicated by a dotted line inFIG. 22. In other words, the reset release interval TRelease isincreased to the same degree as the normal timing, and after the resetnoise is stabilized, the comparator 44 is turned off by the comparatorreset pulse PSET.

The two states are changed smoothly by controlling the pulse width ofthe comparator reset pulse PSET (the auto zero period of time)continuously according to the AD conversion gain or are changed stepwiseby controlling the pulse width of the comparator reset pulse PSET (theauto zero period of time) stepwise according to the AD conversion gain.As a result, when the noise injection is performed, it is possible toadjust the reset release interval TRelease in conjunction with the ADconversion gain by shifting a timing at which the comparator reset pulsePSET is turned off to a previous timing by a degree suitable for the ADconversion gain.

(AD Conversion Gain of Each Color)

As illustrated in FIG. 20, in the CMOS image sensor 101 of FIG. 8, forexample, the color filter of the basic form of the Bayer array is used,and the unit pixels 30 are arranged according to the Bayer array.Further, as described above, the color filters are repeated in units oftwo rows and two columns. Here, the pixel signal is read in units ofrows, and the pixel signal is input to the column AD converting section41 disposed in each vertical signal line 21 for each column, and thusthe pixel signals of only two colors of either R/G or G/B are present inone processing target row.

Thus, the CMOS image sensor 101 can employ a configuration in which aDAC 15 a corresponding to the even-numbered columns and a DAC 15 bcorresponding to the odd-numbered columns are disposed as illustrated inFIG. 23.

The DACs 15 a and 15 b generate a step-like saw-tooth wave (rampwaveform) based on the control signal from the communication timingcontrol section 17. The DACs 15 a and 15 b supply the generatedstep-like saw-tooth waves to the column AD converting sections 41 of thecolumn processing section 14 as reference signals RAMPa and RAMPb.

In other words, in the reference signal generating section 15, when thecontrol signal for generating the reference signals RAMPa and RAMPb issupplied from the communication timing control section 17, the DAC 15 agenerates the reference signal RAMPa that has an inclination βaaccording to a color pixel characteristic of one color (R or G of theeven-numbered column) present on the row control line 20 and has astep-like waveform that is temporally changed in a saw tooth form as awhole. Then, the DAC 15 a supplies the generated reference signal RAMPato the other input terminal of the comparator 44 of the column ADconverting section 41 corresponding to the even-numbered column via thecapacitive element 43.

Similarly, the DAC 15 b generates the reference signal RAMPb that has aninclination βb according to a color pixel characteristic of one color (Gor B of the odd-numbered column) present on the row control line 20 andhas a step-like waveform that is temporally changed in a saw tooth formas a whole. Then, the DAC 15 b supplies the generated reference signalRAMPb to the other input terminal of the comparator 44 of the column ADconverting section 41 corresponding to the odd-numbered column via thecapacitive element 43.

In other words, in the reference signal generating section 15, the DACfor generating the reference signal RAMP is not prepared for all colorsof the color filters in the color separation filter, and the DAC isdisposed in a number according to a combination of certain colorsaccording to a repetition cycle of a color decided according to a typeor an array of a color. Further, when a processing target row isswitched, a combination of certain colors present in the processingtarget row is switched. Thus, in response to the switching, changecharacteristics (for example, the inclinations βa and βb) or initialvalues of the reference signals RAMPa and RAMPb generated by the DACs 15a and 15 b are switched according to characteristics of the colorfilter, that is, characteristics of the pixel signal.

Since the reference signal RAMP is generated for each color as describedabove, the AD conversion gain is changed for each color as well.Further, the AD conversion gain is in conjunction with the control pulseVSLCNT or the like, but since a principle does not change at all even ifthe AD conversion gain is changed for each color, it is possible tocause the control pulse VSLCNT or the like to be in conjunction with theAD conversion gain of each color.

For example, as illustrated in FIG. 23, as the pulse width of thecontrol pulse VSLCNT is adjusted according to the AD conversion gain foreach color, a control pulse VSLCNTa is input to the gate of theswitching transistor 111-1, and a control pulse VSLCNTb is input to thegate of the switching transistor 111-2. As a result, it is possible tocontrol the switching transistors 111-1 and 111-2 individually, average,for example, the outputs of the source followers, or adjust the width ofthe reset level distribution.

Further, the applicant of the present application has already proposedthe technique of switching the reference signal RAMP for each color inJP 2005-328135A (JP 4449565B).

(Another Connection Form of Switching Transistor)

As the connection form of the switching transistor 111, a connectionform other than the connection form illustrated in FIG. 9 may beemployed. FIG. 24 illustrates another connection form of the switchingtransistor 111.

As illustrated in FIG. 24, in a switching transistor 111-1, a gate isconnected with the communication timing control section 17 via thecontrol line 23, a source is connected to the vertical signal line 21-1,and a drain is connected to the row signal line 112. Similarly, in aswitching transistor 111-2, a gate is connected to the control line 23,a source is connected to the vertical signal line 21-2, and a drain isconnected to the row signal line 112.

In this connection form, the switching transistors 111-1 and 111-2perform the switching operation according to the control pulse VSLCNTinput to the gates thereof, so that the vertical signal lines 21-1 and21-2 can be short-circuited.

Further, the connection form of FIG. 24 is an example of anotherconnection form of the switching transistor 111, but any otherconnection form may be employed. In short, it is preferable that theswitching transistor 111 be able to cause the vertical signal lines 21to be short-circuited through the switching operation, and theconnection form between the vertical signal line 21 and the row signalline 112 is arbitrary.

Further, the switching transistor 111 may be connected with all thevertical signal lines 21 (H0, H1, . . . , Hh) or may be connected withsome vertical signal lines 21 (for example, H0, H2, H4, . . . , and thelike of the even-numbered columns) among all the vertical signal lines21 (H0, H1, . . . , Hh). Further, when the switching transistor 111 isconnected with some vertical signal lines 21, for example, the verticalsignal lines 21 may be divided into blocks in a certain unit, and theswitching transistor 111 may be connected with each of the blocks.

Further, the pixel array section 11 may employ a pixel sharingconfiguration in which a plurality of unit pixels 30 arranged in amatrix form share the amplifying transistor 54 and the vertical signalline 21 with other unit pixels.

Further, in this specification, “solid-state” in the solid-state imagingdevice means that it is manufactured using a semiconductor.

Note that application of the present technology is not limited to theapplication to the solid-state imaging device. That is, the presenttechnology is applicable to a general electronic device using asolid-state imaging device for an imaging section (a photoelectricconversion section), the general electronic device including an imagingapparatus such as a digital still camera or a video camera, a mobileterminal device having an imaging function, a copier using a solid-stateimaging device for an image reading section, and the like. Thesolid-state imaging device may be formed as one chip or may be formed asa module having an imaging function in which an imaging section andeither a signal processing section or an optical system are packagedtogether.

<Configuration Example of Electronic Device to Which Present Technologyis Applied>

FIG. 25 is a block diagram of a configuration example of an imagingapparatus serving as an electronic device to which the presenttechnology is applied.

An imaging apparatus 300 in FIG. 25 includes: an optical section 301formed by a lens group or the like; a solid-state imaging device (animaging device) 302 employing the aforementioned configuration of theunit pixels 30, and a DSP (Digital Signal Processor) circuit 303 whichis a camera signal processing circuit. The imaging apparatus 300 alsoincludes a frame memory 304, a display section 305, a recording section306, a manipulation section 307, and a power supply section 308. The DSPcircuit 303, the frame memory 304, the display section 305, therecording section 306, the manipulation section 307, and the powersupply section 308 are connected to each other via a bus line 309.

The optical section 301 takes in incident light (image light) from asubject to form an image on an imaging surface of the solid-stateimaging device 302. The solid-state imaging device 302 converts a lightamount of incident light into an electrical signal on a pixel basis andoutputs the electrical signal, the incident light being used for formingthe image on the imaging surface by the optical section 301. It ispossible to use, as the solid-state imaging device 302, a solid-stateimaging device such as the CMOS image sensor 1 according to theaforementioned embodiment which is arranged on the CMOS image sensor,that is, a solid-state imaging device which makes it possible to capturean image without distortion by using global exposure.

The display section 305 includes a panel display device such as a liquidcrystal panel or an organic EL (Electro Luminescence) panel, anddisplays a moving image or a still image captured by the solid-stateimaging device 302. The recording section 306 records the moving imageor the still image captured by the solid-state imaging device 302 in arecording medium.

The manipulation section 307 issues manipulation instructions forvarious functions of the imaging apparatus 300 in accordance with user'smanipulation. The power supply section 308 appropriately supplies theDSP circuit 303, the frame memory 304, the display section 305, therecording section 306, and the manipulation section 307 with power tocause these sections to operate.

In addition, the aforementioned embodiment has been described by takingas an example the case where the present technology is applied to theCMOS image sensor including the unit pixels 30 arranged in a matrixform, the unit pixels each sensing, as a physical quantity, a signalcharge corresponding to a light amount of visible light. The applicationof the present technology, however, is not limited to the application tothe CMOS image sensor. The present technology is applicable to a generalcolumn-system solid-state imaging device including a column processingsection arranged for each pixel column in a pixel array section.

The application of the present technology is not limited to theapplication to the solid-state imaging device which captures an image bysensing distribution of incident light amounts of visible light. Thepresent technology is also applicable to: a solid-state imaging devicewhich captures an image based on distribution of incidence amounts ofinfrared rays, X-rays, particles or the like; and a general solid-stateimaging device in a broad sense (a physical-quantity distributionsensing device) such as a fingerprint detection sensor which captures animage by sensing distribution of other physical quantities such aspressures or electrostatic capacitances.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof

Additionally, the present technology may also be configured as below.

-   (1) A solid-state imaging device including:

a pixel section configured to include a plurality of pixels arranged ina matrix form, the plurality of pixels performing photoelectricconversion;

column signal lines configured to transmit pixel signals output from thepixels in units of columns;

an AD converting section configured to include a comparator thatcompares a reference signal serving as a ramp wave with the pixelsignals transmitted via the column signal line and convert a referencelevel and a signal level of the pixel signals into digital signalsindependently based on a comparison result of the comparator;

a switch configured to be connected with the column signal lines; and

a control section configured to turn on the switch only during a certainperiod of time in a period of time in which the comparator is reset andcause the column signal lines to be short-circuited.

-   (2) The solid-state imaging device according to (1),

wherein the plurality of pixels are arranged in the pixel section tocorrespond to a color filter in which colors are arranged in a certainrepetitive unit, and

wherein the switch is connected to each column signal line of pixels ofthe same color.

-   (3) The solid-state imaging device according to (1) or (2),

wherein the control section adjusts an ON period of time of the switchaccording to a gain of AD conversion performed by the AD convertingsection.

-   (4) The solid-state imaging device according to any one of (1) to    (3),

wherein the control section adjusts a reset period of the comparatoraccording to the gain of the AD conversion performed by the ADconverting section.

-   (5) The solid-state imaging device according to any one of (1) to    (4),

wherein the gain of the AD conversion performed by the AD convertingsection has a value corresponding to the reference signal differingaccording to each color.

-   (6) The solid-state imaging device according to any one of (1) to    (5),

wherein the switch is a transistor, and

wherein the transistor includes a gate connected to the control sectionvia a control line and a source and a drain that are connected to a rowsignal line connected to the column signal line in a row direction.

-   (7) The solid-state imaging device according to any one of (1) to    (5),

wherein the switch is a transistor, and

wherein the transistor includes a gate connected to the control sectionvia a control line, a source connected to the column signal line, and adrain connected to a row signal line in a row direction.

-   (8) The solid-state imaging device according to any one of (1) to    (7),

wherein the switch is connected with all the column signal lines.

-   (9) The solid-state imaging device according to any one of (1) to    (7),

wherein the column signal lines are divided into blocks in a certainunit, and

wherein the switch is connected with the column signal lines in units ofthe blocks.

-   (10) The solid-state imaging device according to any one of (1) to    (9),

wherein the plurality of pixels arranged in the pixel section in thematrix form share at least an amplifying transistor and the columnsignal lines with other pixels.

-   (11) The solid-state imaging device according to any one of (1) to    (10), further including:

a noise adding section configured to add a noise that is temporallyunchanging and is irregular in a two-dimensional space to the pixelsignals transmitted via the column signal lines.

-   (12) A driving method of a solid-state imaging device, the    solid-state imaging device including

a pixel section configured to include a plurality of pixels arranged ina matrix form, the plurality of pixels performing photoelectricconversion,

column signal lines configured to transmit pixel signals output from thepixels in units of columns,

an AD converting section configured to include a comparator thatcompares a reference signal serving as a ramp wave with the pixelsignals transmitted via the column signal line and convert a referencelevel and a signal level of the pixel signals into digital signalsindependently based on a comparison result of the comparator, and

a switch configured to be connected with the column signal lines,

the driving method including:

a step of, by the solid-state imaging device, turning on the switch onlyduring a certain period of time in a period of time in which thecomparator is reset and causing the column signal lines to beshort-circuited.

-   (13) An electronic device including:

a solid-state imaging device including

a pixel section configured to include a plurality of pixels arranged ina matrix form, the plurality of pixels performing photoelectricconversion,

column signal lines configured to transmit pixel signals output from thepixels in units of columns,

an AD converting section configured to include a comparator thatcompares a reference signal serving as a ramp wave with the pixelsignals transmitted via the column signal line and convert a referencelevel and a signal level of the pixel signals into digital signalsindependently based on a comparison result of the comparator,

a switch configured to be connected with the column signal lines, and

a control section configured to turn on the switch only during a certainperiod of time in a period of time in which the comparator is reset andcause the column signal lines to be short-circuited.

REFERENCE SIGNS LIST

-   1, 101 CMOS image sensor-   11 pixel array section-   13 read current source section-   14 column processing section-   15 reference signal generating section-   15 a, 15 b DAC-   17 communication timing control section-   19 noise adding section-   20 row control line-   21 vertical signal line-   23 control line-   30 unit pixel-   41 column AD converting section-   42 capacitive element-   43 capacitive element-   44 comparator-   45 counter-   54 amplifying transistor-   110 switch-   111 switching transistor-   112 row signal line-   300 imaging apparatus-   302 solid-state imaging device

What is claimed is:
 1. A solid-state imaging device comprising: a pixelsection configured to include a plurality of pixels arranged in a matrixform, the plurality of pixels performing photoelectric conversion;column signal lines configured to transmit pixel signals output from thepixels in units of columns; an AD converting section configured toinclude a comparator that compares a reference signal serving as a rampwave with the pixel signals transmitted via the column signal line andconvert a reference level and a signal level of the pixel signals intodigital signals independently based on a comparison result of thecomparator; a switch configured to be connected with the column signallines; and a control section configured to turn on the switch onlyduring a certain period of time in a period of time in which thecomparator is reset and cause the column signal lines to beshort-circuited, wherein the plurality of pixels are arranged in thepixel section to correspond to a color filter in which colors arearranged in a certain repetitive unit, and wherein the switch isconnected to each column signal line of pixels of the same color.
 2. Thesolid-state imaging device according to claim 1, wherein the controlsection adjusts an ON period of time of the switch according to a gainof AD conversion performed by the AD converting section.
 3. Thesolid-state imaging device according to claim 2, wherein the controlsection adjusts a reset period of the comparator according to the gainof the AD conversion performed by the AD converting section.
 4. Thesolid-state imaging device according to claim 3, wherein the gain of theAD conversion performed by the AD converting section has a valuecorresponding to the reference signal differing according to each color.5. The solid-state imaging device according to claim 1, wherein theswitch is a transistor, and wherein the transistor includes a gateconnected to the control section via a control line and a source and adrain that are connected to a row signal line connected to the columnsignal line in a row direction.
 6. The solid-state imaging deviceaccording to claim 1, wherein the switch is a transistor, and whereinthe transistor includes a gate connected to the control section via acontrol line, a source connected to the column signal line, and a drainconnected to a row signal line in a row direction.
 7. The solid-stateimaging device according to claim 1, wherein the switch is connectedwith all the column signal lines.
 8. The solid-state imaging deviceaccording to claim 1, wherein the column signal lines are divided intoblocks in a certain unit, and wherein the switch is connected with thecolumn signal lines in units of the blocks.
 9. The solid-state imagingdevice according to claim 1, wherein the plurality of pixels arranged inthe pixel section in the matrix form share at least an amplifyingtransistor and the column signal lines with other pixels.
 10. Thesolid-state imaging device according to claim 1, further comprising: anoise adding section configured to add a noise that is temporallyunchanging and is irregular in a two-dimensional space to the pixelsignals transmitted via the column signal lines.
 11. A driving method ofa solid-state imaging device, the solid-state imaging device including apixel section configured to include a plurality of pixels arranged in amatrix form, the plurality of pixels performing photoelectricconversion, column signal lines configured to transmit pixel signalsoutput from the pixels in units of columns, an AD converting sectionconfigured to include a comparator that compares a reference signalserving as a ramp wave with the pixel signals transmitted via the columnsignal line and convert a reference level and a signal level of thepixel signals into digital signals independently based on a comparisonresult of the comparator, and a switch configured to be connected withthe column signal lines, the driving method comprising: a step of, bythe solid-state imaging device, turning on the switch only during acertain period of time in a period of time in which the comparator isreset and causing the column signal lines to be short-circuited, whereinthe plurality of pixels are arranged in the pixel section to correspondto a color filter in which colors are arranged in a certain repetitiveunit, and wherein the switch is connected to each column signal line ofpixels of the same color.
 12. An electronic device comprising: asolid-state imaging device including a pixel section configured toinclude a plurality of pixels arranged in a matrix form, the pluralityof pixels performing photoelectric conversion, column signal linesconfigured to transmit pixel signals output from the pixels in units ofcolumns, an AD converting section configured to include a comparatorthat compares a reference signal serving as a ramp wave with the pixelsignals transmitted via the column signal line and convert a referencelevel and a signal level of the pixel signals into digital signalsindependently based on a comparison result of the comparator, a switchconfigured to be connected with the column signal lines, and a controlsection configured to turn on the switch only during a certain period oftime in a period of time in which the comparator is reset and cause thecolumn signal lines to be short-circuited, wherein the plurality ofpixels are arranged in the pixel section to correspond to a color filterin which colors are arranged in a certain repetitive unit, and whereinthe switch is connected to each column signal line of pixels of the samecolor.
 13. (canceled)